This invention relates generally to gas turbine engines, and specifically to aviation applications. In particular, the invention concerns a gas turbine engine for an aircraft.
Gas turbine engines (or combustion turbines) are built around a power core made up of a compressor, combustor and turbine, arranged in flow series with an upstream inlet and downstream exhaust. The compressor compresses air from the inlet, which is mixed with fuel in the combustor and ignited to generate hot combustion gas. The turbine extracts energy from the expanding combustion gas, and drives the compressor via a common shaft. Energy is delivered in the form of rotational energy in the shaft, reactive thrust from the exhaust, or both.
Gas turbine engines provide efficient, reliable power for a wide range of applications, including aviation and industrial power generation. Small-scale engines including auxiliary power units typically utilize a one-spool design, with co-rotating compressor and turbine sections. Larger-scale jet engines and industrial gas turbines (IGTs) are generally arranged into a number of coaxially nested spools, which operate at different pressures and temperatures, and rotate at different speeds.
The individual compressor and turbine sections in each spool are subdivided into a number of stages, which are formed of alternating rows of rotor blade and stator vane airfoils. The airfoils are shaped to turn, accelerate and compress the working fluid flow, and to generate lift for conversion to rotational energy in the turbine.
Aviation applications include turbojet, turbofan, turboprop and turboshaft engines. In turbojet engines, thrust is generated primarily from the exhaust. Modern fixed-wing aircraft generally employ turbofan and turboprop engines, in which the low pressure spool is coupled to a propulsion fan or propeller. Turboshaft engines are typically used on rotary-wing aircraft, including helicopters.
Turbofans are commonly divided into high and low bypass configurations. High bypass turbofans generate thrust primarily from the fan, which drives airflow through a bypass duct oriented around the engine core. This design is common on commercial aircraft, where noise and fuel efficiency are primary concerns. Low bypass turbofans generate proportionally more thrust from the exhaust flow, providing greater specific thrust for use on supersonic fighters and other high-performance aircraft.
As commercial engines trend toward higher bypass ratios, fuel efficiency is increased and noise is reduced. Specific thrust is also lower, however, and the fan inlet diameter gets larger, increasing engine size and weight. Very high and ultra high bypass ratio engines thus present design challenges, particularly for aft-mounted configurations where there is less available area than on the wing.